Stasis does not falsify evolution

Every week people submit letters to the editor of American newspapers on the subject of evolution. Many readers argue that evolution never happened, and in doing so they often present one or more of a sleuth of standard anti-evolution arguments. I just revisited two of them, and here is another very common one. This one more plainly than most others illustrate the ignorance of those who put it forth:

The theory [of evolution] says that things evolve over time, If that is correct then why have some species not evolved at all! Several fish have stayed the same. The crocodile has adapted and grown smaller in size but it is still a crocodile. Marine turtles have not changed according to the fossil record. Those are just a couple of examples that have been observed.

I found this in the comments of this letter to the editor of a Tennessee paper in defense of evolution, written as a reply to another letter that asserted that evolution is a religion.

The argument has also recently been trampled to death by Adnan Oktar, aka Harun Yahua, who produced the now infamous Atlas of Creation. In that beautifully illustrated tome (though some pictures are of fishing lures) he similarly argued that since many species are identical to fossils that are millions of years old, these didn't evolve (as they falsely claim that the theory of evolution posits they must), and thus evolution is false.

Within evolutionary theory, the phenomenon of no phenotypic or genotypic change is known as stasis. Wikipedia does not have an article on stasis, unfortunately, so you'll have to make do with the mention of the it under the heading of punctuated equilibrium (stasis has also been called unpunctuated equilibrium, but don't let me hear that again!). Essentially, at times organisms/populations/species evolve rapidly (as is the case with Podarcis sicula), and at times hardly at all (as with the Coelacanth and other living fossils).

Why does stasis happen? Stasis occurs when

the environment that the organism lives in doesn't change, or

the organism is developmentally constrained so that it can't evolve.

[Update 10/25/2012: Stasis could also be explained by

habitat tracking: populations whose environment changes can physically move so that they are not going to be affected by the change, and

small populations may not be able to respond to selection because it isn't strong enough; instead, in small populations genetic drift rules.

The last two reasons could work at the same time, even in conjunction with developmental constraints.]

Developmental constraint is a little harder to explain, but I promise myself to deal with it thoroughly within very long.

On the contrary, the idea that stasis prevails when the environment doesn't change is really easy to grasp. It is the environment that determines what the fittest phenotype is, so when the environment doesn't change, neither does the organism (except for neutral evolution, in which genotypic changes that doesn't not affect the fitness of the organism can go to fixation).

In terms of fitness landscapes: If you're sitting at the top of a peak, then any phenotypic change lowers your fitness, and stasis results. This is one effect of natural selection: it weeds out the inferior phenotypes, preserving the type that produces the most offpsring (there are other effects of selection, by the way). As long as that landscape doesn't change, the peaks remains, and evolution doesn't happen.

Ahh, excellent! That should take care of that, and I suspect we won't hear that silly argument made ever again...

P.S. Yes, I love Wikipedia.

15 comments:

I just heard three days of it at the State Board of Education hearings in Austin, Tx. where the board was deciding what standards should be included in the public schools teaching of evolution.The creationist members of the board seemed quite smug that this 'stasis argument' totally dismantled evolution.Scientist after scientist testified and basically used the same rebuffs as you did, but the creationists couldnt grasp it.You could see they were simply confused by the scientific explanation.I know they have a certain agenda, but also realized they simply couldn't grasp the big overview and enormity of change over time. Brian Rutledge Brutle6859@aol.com

The Texus SBOE allows public discussion( three days on this topic)before they vote and I signed up to give my three minutes worth.My background is in biology and chemistry, then went on to get my M.D.. Many real research scientists were there as well.The Discovery Institute was well represented as well.Not sure why they would even be allowed to testify at a Texas hearing, but creationists on the board invited them.It was obvious that none of the board members really understood science and not one could define what a scientific theory is or how it is different from the laymans use of the term.The hard core board members are deeply ingrained in the Discovery Institute and Answers in Genesis propaganda and I think really believe it.Of course their rigid dogmatic thought process makes them easy prey to such beliefs. They use the same old tired arguments and have obviously been well schooled by the 'experts'. They simply rejected comments from the many scientists who testified,partly because it was offensive to their religious beliefs and partly because not one of them had an inkling of scientific background or education.They are elected by the public.The only thing that can be done is vote them out of office next election cycle. Your last question is a great one, but they have a very shallow idea of what evolution entails, so these pseudoscientific arguments they use ACTUALLY make sense to them.My analogy would be me sitting next to an astrophysicist and trying to grasp what he/she is saying. If it offended some deep ideologic belief I had,I could easily throw up some pseudo garbage that might sound credible to a layman.All eight major universities(Rice,Texas,Texas A&M,SMU,TCU,Baylor,Trinity)sent scientists and they were rebuffed. Was hard to watch and not representative of our state.No one knew these board members were such ideologues until this came up. There is great public furor.I think the only good thing that came out of this is public awareness and hopefully next voting cycle will rectify things.We felt like Clarence Darrow at the Scopes trial Brian

Heres a new tactic the Discovery folks are now preaching to the lemmings. Tell me if you have heard of this one. They start by attacking common ancestry by using the fossil record. but heres the twist-they make the claim that the fossil record really has no proof of common ancestry because it doesnt say anything about the "process" of how evolution works.Of course it doesnt because the "process" is explained by natural selection,genetic drift etc.But no one caught that except the scientists and they had already testified.I wanted to scream out that the fossil record is like a photo of the past and never claims to deal with process. the Discovery Institute loves this new dishonest example of why the concept of common ancestry is a fallicy. Ever heard of that one?They even got two scientists to answer yes or no and then cut them off before they could expose the fraud. Brian

The hard core board members are deeply ingrained in the Discovery Institute and Answers in Genesis propaganda and I think really believe it.

Brian, this is a really funny observation, because the DI and AiG are very much at odds with each other. IDers don't believe in YEC, and people at AiG don't believe that anything EVER evolved, which people at DI will admit to.

Evolution is about random mutations and natural selection processes at work; so why would there need to be an environmental change for evolution to occur?Evolution is: random mutations taking place in genes; these mutated genes are then passed on to the next generation. If these new mutated genes are advantageous, then the animal who acquired them becomes fitter for survival than the rest, i.e. gets selected naturally. You do not need an environmental change for mutations to occur, nor you need an environmental change for natural selection to occur. So where do evolutionist come with the argument that statis is a result of a non-changing environment?

Evolution is about random mutations and natural selection processes at work; so why would there need to be an environmental change for evolution to occur?Thanks for the question.

Natural selection has everything to do with the enviroment. It is the environment the organisms adapt to, see.

The reason that evolution stops when the environment doesn't change is that after the pupolation has adaptated to that environment, there is no improvement possible. Imagine climbing to the top of a hill: from there the only way is down. There are no more beneficial mutations to be found, so mutated genes aren't more advantageous than the ones that already exist at that point.

However, a fitter phenotype could still be found, but the genotype for that might require crossing valleys in the fitness landscape, which in the short term is not favored, and thus the fitter genotype can't evolve (usually).

I could also answer that your understanding of evolutionary theory is incomplete, and that you should be required to learn something more before telling others what evolution is.

Natural selection has everything to do with the environment. It is the environment the organisms adapt to, see..

Very true; and this is where my argument exactly comes from. From the evolution perspective, if organisms acquire new characteristics, through random genetic mutations, which make them more adaptive to the environment they live in, then they will evolve, regardless of whether the environment has changed or not.

The reason that evolution stops when the environment doesn't change is that after the population has adaptated to that environment, there is no improvement possible. When it comes to improvements, in any thing you can imagine, only the sky is the limit. As far as the material world is concerned, nothing is perfect; and as long as that is the case, there is always room for improvement. When a population has adapted to a certain environment, there is no reason for not becoming MORE adapted to that environment; after all, that is what evolution is all about; i.e. becoming more adapted and hence evolve.

Imagine climbing to the top of a hill: from there the only way is down. There are no more beneficial mutations to be found, so mutated genes aren't more advantageous than the ones that already exist at that point.When it comes to the environment we live in, there is no top-of-a-hill here. What can swim can evolve to walk on land, what can walk on land can evolve to fly, what can fly can evolve to swim, what is blind can evolve to have eyes, what is small can evolve to big, what is big can evolve to small, what has no claws and speed to hunt can evolve to one that has, what can only eat plants can evolve to one that can eat both plants and animals, what needs so much food to survive can evolve to one that needs less food, and so on. As long as survival advantage and better adaptation are concerned, there is always room for improvement.

If a population of organism was to evolve, via random mutations and natural selection, it will give no thought of what impact its evolution will have on the surrounding environment and other organisms in the long run. In other words, as long as there are adaptation advantages to be gained, then they should be gained, if evolution theory was to be true.

I could also answer that your understanding of evolutionary theory is incomplete, and that you should be required to learn something more before telling others what evolution is.This is a typical accusation that creationists get from evolutionists; and that is, lack of understanding of the theory of evolution. What is it that I need to do, as an educated person, in order to fully understand the theory of evolution, if reading about evolution alone does not serve the purpose? What makes it difficult to grab the theory of evolution? For years now I’ve been surfing the web, and as far as I remember, there are two mechanisms of evolution: random mutations and natural selection. This is what is always being taught about evolution, by evolutionist scientists themselves. I’m not teaching evolution here; I’m just expressing my understanding of evolution, which I acquired from reading several articles on evolution.

The driving forces of evolution are indeed: random mutations and natural selection; not environmental changes. Had evolution occurred, billions and billions of random mutations must have taken place, throughout hundreds of millions of years, with natural selection as the guiding force, from a simple one-cell organism to very complex organisms.

If you’re telling me that every time one or some of these billions of mutations took place, there must have been an environmental change, without which, natural selection could not have played a roll, then there must have been millions of environmental changes throughout history.

If there were millions of environmental changes throughout history; i.e. so frequent, how come the environments in which the organisms that did not evolve stayed the same? Note that this question is similar to the question on stasis, and that was, how come some organisms stayed the same, over a period of hundreds of millions of years, while the rest undergone millions of changes?

If you’re telling me that, an environmental change is not always required for evolution to occur, then the question would again be, why some organisms stayed the same for hundreds of millions of years?

You say, When it comes to improvements, in any thing you can imagine, only the sky is the limit.That's only in principle. In reality these fitter genotypes are very, very difficult to evolve. They require a genetic reorganization that is detrimental to the organisms in the short term, and which therefore will be outcompeted by the individuals that do not make those changes.

What is it that I need to do, as an educated person, in order to fully understand the theory of evolution, if reading about evolution alone does not serve the purpose? What makes it difficult to grab the theory of evolution? For years now I’ve been surfing the web, and as far as I remember, there are two mechanisms of evolution: random mutations and natural selection.If your present understanding is that all there is to evolution is mutation and natural selection, then you clearly have not read enough. On top of that, you seem to not fully understand the relationship between mutation, selection, and the environment. For starters, you should know about genetic drift and gene flow. Together with those two, mutation and selection are the four mechanism that governs genetic variation within populations.

I am very curious about which books and articles you have read. Would you be willing to supply a list? If so, we could actually talk about how to proceed. If nothing else, I recommend reading Evolutionary Biology by Douglas Futuyma.

If you're specifically interested in the problem of stasis, try this paper by Hansen and Houle on the subject.

Human try to fly . But they dont develop wing. When dino try to fly, they develop wing and becomes bird.Why?

The word is "evolve", not develop. Biologically those are very different things.

The dinosaurs did not evolve wings because they tried to fly. Some dinosaurs evolved wings over many generations, probably by gaining an advantage either by initially gliding (trees down) or being able to run up steep inclines (ground up).

You should acknowledge that the evidence that birds evolved from dinosaurs is plentiful, but that there is some evidence that points to another conclusion. So, believe that birds descended directly from dinosaurs with a higher probability than the other hypothesis (which posits that the many shared traits between birds and dinosaurs are not homologous, i.e., that they evolved independently).

I'm not very good at biology and neither good at english, but I'll try to contribute.

So, think of some cave dwelling crabs. They loose the ability to see and their pigments. If one day one of the crabs suddenly had re-evolved light sensitive cells in their eyes, that would not bring an advantage to that crab + maybe as a redundancy even cost extra energy.

Yes, that makes sense. In that case those individuals who re-evolved sight would be at a disadvantage, and sight would then most likely not spread in the population (at least while they lived in caves).

Pleiotropy comes from the Greek πλείων pleion, meaning "more", and τρέπειν trepein, meaning "to turn, to convert". It designates the occurrence of a single gene affecting multiple traits, and is a hugely important concept in evolutionary biology.

I'm a postdoc at UC Santa Barbara.

All Many aspects of evolution interest me, but my research focus is currently on microbial evolution, adaptive radiation, speciation, fitness landscapes, epistasis, and the influence of genetic architecture on adaptation and speciation.